Tripping devices for power system circuit breakers have generally been of one of two forms, i.e., either an electro-mechanical induction disc relay or an electronic inverse overcurrent relay. The electronic inverse overcurrent relays have proved to be superior to the induction disc relay in terms of accuracy, flexibility, temperature stability, reduced maintenance, absence of overtravel and fast reset. Inverse overcurrent relays are most frequently coordinated with fuses. However, electronic inverse overcurrent relays have a time current characteristic in which operating time is inversely proportional to the first power of current and fuses inherently have a time current characteristic (TCC) in which operating time is inversely proportional to about the second power of current. Complex circuits are therefore required to make the actual time current characteristic of the electronic inverse overcurrent relay approximate the time current characteristic of the fuse.